Crystal Ball at MAMI

Daniel Watts, Univ. of Edinburgh (UK)

For the CB@MAMI Collaboration

(mainly involving low cross sections and/or precision measurements)

• Precision spectroscopy of low lying baryon states:

(1232)) from p’p and ’n

(S11(1535)) from p’p reaction

• Threshold meson production: (test of LET/ ChPT):

Strangeness (N →K)

0 photoproduction at threshold

• Ambiguity free amplitude analysis of meson photoproduction

Requires Double polarization measurements:

N→N(); N (,…) channels

• Tests of fundamental symmetries (C,CP,CPT…)

Rare / decays

• In medium properties of hadrons & nuclear physics:

Meson photo production on nuclei

CB@MAMI: Main physics objectives

• 100% duty factor electron microtron

• MAMI-C 1.5 GeV upgrade (2006)

(MAMI-B 0.85 GeV)

• Crystal Ball - A2 hall

(tagged photon beam)

The MAMI facility

One of the MAMI-C magnets

e

Photon Tagger upgrade

Emax

(GeV)

Imax

(s-1MeV-

1)

ΔE

(FWHM(MeV)

Pollin

(%)

Polcir

c

(%)

3.5 ≈ 104 5 70 80

1.5 ≈ 103 15 100 100

5.4 ≈ 104 5 70 80

0.45 ≈ 103 5 100 100

0.81.5

≈ 105 1 70 80

3.0 ≈ 103 30 100 100

Photon beam facilities

Legs

B

C

1976 Conceived1978 -1981SPEAR(Ecm = 3 - 7 GeV)

1982-1986DORIS (Ecm = 9 -10 GeV)

1996-2002 BNL-AGS (Ecm = 1.2 – 1.53 GeV)

2002MAMI (Ecm = 1.2 -1.9 GeV)

Crystal Ball history

Crystal Ball arrives at Frankfurt

Good angular and energy resolution, close to 4 acceptance

Setup at MAMI

Tracker & Particle-ID

Tracker & Particle-ID

~ 1.5o

~ 1.3o

• Two cylindrical wire chambers• 480 anode wires, 320 strips• Adapted from DAPHNE• New MWPC tracker under construction (2006)

2mm thickEJ204 scintillator

320m

m

MWPC & Particle-ID in situ

Good angular and energy resolution, close to 4 acceptance

Setup at MAMI

Tracker & Particle-ID

MAMI Photo GalleryCBwith PMTs

CB

Panoramic view of MAMI setup

TAPS CB

TAPS

Targets at MAMI

Liquid hydrogen (deuterium) target

Liquid 3He target (2006)

Polarised 3He gas target(~2008)

Frozen spin Targetbutanol / deuterated butanol

(~2007)

Apr '05-Jan'06 : MAMI-C upgrade, photon tagger upgrade

'06 onwards : Second production runs E=0.1-1.5 GeV: unpolarized, polarised, nuclear targets

Nov '02: Crystal Ball moved to MainzNov '03: Crystal Ball installed at photon beam at MAMIMar '04: TAPS installedApr '04: MWPC and PID installedMay '04: First test run tests with the complete setupJun'04-Apr '05 : First production runs

CB@MAMI – timetable

E=0.1-0.8 GeV: unpolarized H2 or D2 targets, nuclear targets

Selection of preliminary spectra from first round of

experimentsE= 0.1 – 0.8 GeV

Preliminary analyses: identification

→MeV

→MeV

→→MeV

Preliminary analyses: Ags(0)Ags

coherent 0 photoproduction from nuclei

208Pb

33o

sin ~ 1.22 /D Rm ~ 5.75 fm(Rc ~ 5.50 fm)

E=220 MeV

16O12C 40Ca

4.4 MeV3.7MeV

6.1 MeV

Also see coincident low energy Nuclear Decay Photons !!

• Clear diffraction patterns for 208Pb, 40Ca, 16O, 12C

d/dA2(q/k)P32|F

m(q)|2sin2

• Matter form factor, properties in the medium

C. Tarbert, D. Watts

Photon Asymmetry :

)2cos(1)(),(

p

d

d

d

d

Preliminary analyses: (, p)0

A. Starostin

• High statistics measurement

• With beam polarisation → , circ

~5% of total s

tatistic

s

Preliminary analyses: p(,p)

dependence ofyield (not acc. corrected)

F.Zehr

Preliminary analyses: p(,p)to measure

p p

´

p

p

´

p p

´

+

+

coherent addition...

small

dominant

MAMI pilot measurement with TAPS onlyM. Kotulla et al., PRL 89 (2002) 272001

• 100 in statistics • measure beam polarisation observables • Both p0 and n+ decay of +

=5p=3p=1p

= 0.79p

=3p

p(,p)to measure

Future planswith MAMI-C

E= 0.1 – 1.5 GeV

Double-polarisation in pseudo-scalar meson photoproduction

Polarisation of

target recoil

Observable

p → p 0 p → p

n → n 0 n → n

Circularly polarised photons + longitudinally polarised protons (or neutrons)

Deuterated butanol frozen spin target

Butanol frozen spin target

Beam-target observable: E

Previous E measurement for p → p 0 led to significant revision of helicity amplitudes for D13(1520) [ PRL 88, 232002 (2002)]

Neutron targets: different resonance contributions, isospin structure

Also get channels – mechanisms, contributions to GDH integrand

Expected data accuracy10o

E±10 MeV250 hrs

p → p 0

=90o

n → n 0

=90o

E

E(MeV) E(MeV)

Variable well suited to studies of Roper resonance ( P11(1440) )

p → p 0 p → n +

linearly polarised photons + longitudinally polarised protons

Beam-target observable: G

Expected Data accuracy10o

E±10 MeV600 hrs

Beam-Recoil Observables: Cx, OX, T, P

Graphite sheet(~7cm thick)

TAPS

Crystal Ball

beam

Hydrogen target cell

Initial path of proton Polarimeter acceptance : ±20o polar angle (target at centre)Most events suffer only coulomb scattering

Useful scattered eventSelect events with scattering angleslarger than ~10 degrees : arising from nuclear interaction

n() =no(){1+A()[Pycos()–Pxsin()]

Beam-Recoil Observables- p()p

300 hrs Ee=0.85 GeV

500 hrs Ee=1.5 GeV

(cm)=130o

~4 detector system

Very good neutral (and charged) particle detection capabilities

Excellent properties of MAMI beam

Availability of polarized targets

Recoil nucleon polarimetry possibilities

High quality data for meson photoproduction for E up to ~1.5 GeV can be expected

Summary

J.Brudvik, J. Goetz, B.M.K.Nefkens, S.N.Prakhov, A.Starostin, I. Saurez, University of California, Los Angeles, CA, USA

J.Ahrens, H.J.Arends, D.Drechsel, D.Krambrich, M.Rost, S.Scherer, A.Thomas, L.Tiator, D. von Harrach and Th.Walcher Institut fur Kernphysik, University of Mainz, Germany

R. Beck, M. Lang, A. Nikolaev, S. Schumann, M. unverzagt, Helmholtz-Institut fur strahlen und Kernphysik, Universitat Bonn, Germany

S.Altieri, A.Braghieri, P.Pedroni, A.Panzeri and T.Pinelli INFN Sezione di Pavia and DFNT University of Pavia, Italy

J.R.M.Annand, R.Codling, E.Downie, D.Glazier, J. Kellie, K.Livingston, J.McGeorge, I.J.D.MacGregor, R. Owens D.Protopopescu and G.Rosner Department of Physics and Astronomy, University of Glasgow, Glasgow, UK

C.Bennhold and W.Briscoe George Washington University, Washington, USA

S.Cherepnya, L.Fil'kov, and V.Kashevarow Lebedev Physical Institute, Moscow, Russia

V.Bekrenev, S.Kruglov, A.Koulbardis, and N.Kozlenko Petersburg Nuclear Physics Institute, Gatchina, Russia

B.Boillat, B.Krusche and F.Zehr, Institut fur Physik University of Basel, Basel, Ch

P. Drexler, F. Hjelm, M. Kotulla, K. Makonoyi, R.Novotny, M. Thiel and D. Trnka II. Phys. Institut, University of Giessen, Germany

D.Branford, K.Foehl, C.M.Tarbert and D.P.Watts School of Physics, University of Edinburgh, Edinburgh, UK

V.Lisin, R.Kondratiev and A.Polonski Institute for Nuclear Research, Moscow, Russia

J.W. Price California State University, Dominguez hills, CA, USA

D.Hornidge Mount Allison University, Sackville, Canada

P. Grabmayr and T. Hehl Physikalisches Institut Universitat Tubingen, Tubingen, Germany

D.M. Manley Kent State University, Kent, USA

M. Korolija and I. Supek Rudjer Boskovic Institute, Zagreb, Croatia

D. Sober Catholic Catholic University, Washington DC

M. Vanderhaeghen, College of William and Mary, Williamsburg, USA

CB@MAMI

(mainly involving low cross sections and/or precision measurements)

• Precision spectroscopy of low lying baryon states:

(1232)) from p’p and ’n

m(S11(1535)) from p’p reaction

• Threshold meson production: (test of LET/ ChPT):

Strangeness (N →K)

0 photoproduction at threshold

• Ambiguity free amplitude analysis of meson photoproduction

Requires Double polarization measurements:

N→N(); N (,…) channels

• Tests of fundamental symmetries (C,CP,CPT…)

Rare decays

• In medium properties of hadrons:

Meson photo production on nuclei

CB@MAMI: Main physics objectives

• 100 in statistics • measure beam polarisation observables • Both p0 and n+ decay of +

=5p=3p=1p

= 0.79p

=3p

p(,p)to measure

• 4 complex amplitudes – 16 observables in meson photoproduction

• Each double polarisation observable gives different combination of amplitudes

• To fix the 4 amplitudes unambiguously → 8 real quantities

• Cannot choose from the same set

Polarisation of

target recoil

Double-polarisation: theory background

Observable

• Predicted sensitivity to poorly established resonances

• Resonance parameters from quark model (Capstick and Roberts)

Solid – SAIDDashed – background + **** Dotdash- background + **** +N-

3/2(1960)

Dutta, Gao and Lee, PRC 65, 044619 (2002)

Cx’ ( + recoil) – theoretical predictions

P

T

Previous experimental data – SAID database

Data for all CM breakup angles

Ox’ Cx’

Recent JLAB datanot in database

• First determination p(,p)0 in 2002Hall A JLab

• MAID & SAID poor description of new data

Recent Cx’ measurement at JLab

Po

lari

sati

on

tra

nsf

er C

x’

Photon energy (MeV)

The proposed experimental setup

Graphite sheet

TAPS

Crystal Ball

beam

Hydrogen target cell

Initial path of proton Polarimeter acceptance : ±20o polar angle (target at centre)Most events suffer only coulomb scattering

Useful scattered eventSelect events with scattering angleslarger than ~10 degrees : arising from nuclear interaction

n() =no(){1+A()[Pycos()–Pxsin()]

GEANT simulation of polarimeter

No GraphiteWith Graphite scatterer

• Simulation includes realisticsmearing of energy deposits due to experimental energy resolutionand proper cluster finding algorithms

• Finite target size and E resolution included

Angle between N(E,) and TAPS hit

CM) >~130o

E=150 MeVE=200Eg=300E=500E=750E=1000E=1500

Polarimeteracceptance

Nucleon angle in lab (deg)

Pio

n a

ngle

in C

M (

deg)

Kinematic acceptance of polarimeter

p()N

• More forward recoils than for pion production.

• Almost all recoils are incident on polarimeter up to ~0.8 GeV

Eg=720Eg=820Eg=920Eg=1520

Lab nucleon angle (degrees)

CM

a

ng

le (

deg

rees)

Polarimeter acceptance

Kinematic acceptance of polarimeter

p()N

Cx’ – Extraction and expected accuracy

Plot difference in distributions for two helicity states (cut on region of with reasonable A())

Left with simple sin() Dependence. Extract Px

0 180 360

Photon energy (MeV)

Cx’

P=0.7, E=±25MeV, =130±10

~ 1 b/sr → Cx ~ 0.015

~ 0.1 b/sr → Cx ~0.05

Greatly improved data quality

• Measure direction of nucleon before and after the scatterer with sufficient accuracy to determine an analysing reaction has taken place.

Polarimetry basics

For incident protons also have multiple (coulomb) scattering

scat=5-20o

scat

• Magnetic dipole moments:

(1232) from p’p and ’n

S11(1535) from p’p) reaction

• Threshold meson production: (test of LET/ ChPT):

Strangeness (N →K)

0 photoproduction at threshold

• Double polarization measurements: (properties of baryon resonances/GDH)

N→N(); N (,…) channels

• Mass of -meson and rare decays

• Meson photo production on nuclei: medium mod., nuclear properties

CB@MAMI: Future programme

• 4 complex amplitudes →16 observables in meson photoproduction

→ need 8 well chosen measurements to fix the 4 amplitudes

• Each double polarisation observable gives a different combination of amplitudes

Polarisation of

target recoil

Double-polarisation in pseudo-scalar

meson photoproduction

Observable

MWPC tracker

~ 1.5o

~ 1.3o

• Adapted from MWPCs used with the DAPHNE detector

• New dedicated MWPC tracker under construction(Complete early 2006)

Scattered nucleon detection in TAPS

• 1 TAPS block ~ position resolution for hit

• TAPS~0.9m from scatterer

N

Straight through10o scatter20o scatter

Detrimental side-effects of scatterer material

• To hit polarimeter TN>100 MeV in (p,)N above the

• Proton energy loss

<10 MeV for Tp>100 MeV.

• Multiple scattering

<1o FWHM for Tp>100 MeV

• 0.37 radiation lengths conversion ~ 30%

Tp incident proton (MeV)

Tp e

xit

pro

ton

(M

eV

)

Tp after graphiteEnergy loss

0

0.5

1

1.5

2

2.5

3

0 200 400 600 800 1000 1200

Series1

Coulomb scattering

Proton energy (MeV)FW

HM

scatt

eri

ng

an

gle

(d

eg

)

1976 Conceived1978 -1981SPEAR(Ecm = 3 - 7 GeV) spectroscopyradiative decays decaysD decays, → f

1982-1986DORIS (Ecm = 9 -10 GeV)Y spectroscopyradiative decays

1996-2002 BNL-AGS (Ecm = 1.2 – 1.53 GeV) decays, medium. mod

2002MAMI (Ecm = 1.2 -1.9 GeV)

Crystal Ball history

24 of 2x10x320mm EJ204 scintillator

24 Hamamatsu =10mm PMT

Particle-ID detector

Small light attenuation

Good separation of p, with little overhead in

material before MWPC and CB

detectors

Hadron Structure: + Magnetic Moment

recent calculation:W.-T. Chiang, M. Vanderhaeghen, S. N. Yang, D. Drechsel, PRC 71,015204 (04)

includes N rescattering loops

Hadron Structure: + Magnetic Moment

Connection between N’N and NN

).(1

'0

' 'factorkin

d

d

EddE

dE

p n

Hadron Structure: + Magnetic Moment

''

1

EdE

dR

M. Kotulla et al., PRL 89 (2002) 272001

TAPS – first

p → p ’ data

)(0.3)(5.1)(2.17.2 model sysstat

=1=7

(units: N)

(units: N)

Hadron Structure: + Magnetic Moment

sensitivity to angular differential cross section with cut on ´ energy

sensitivity to beam asymmetry (linearly polarized photon beam)

N )1(

Good angular and energy resolution, close to 4 acceptance for charged and neutral final states

Setup at MAMI